Index means to guide something. Some further information can be had through index. An index is an indicator, indicating any subject-matter. In filing, index helps the location of any letter, record, files, etc. Thus it provides quick reference, which is essential of a good filing system.
An index can be seen in almost all books, in last pages. There, the index will indicate the page number, where the particular subject is dealt with. In the same way, in filing system the index is much helpful to locate the files needed.
In a concern, various files are maintained for different departments and different topics. Therefore, to locate the files, the index as an indicator is inevitable.
Classification and indexing are not the same. Classification is a method of filing and the manner in which the files of different subjects are arranged. Indexing is a method of making reference to the files. “An index is a finding tool. It furnishes the key as to how the materials are arranged.